mm/kfence/kfence.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * Kernel Electric-Fence (KFENCE). For more info please see
   4  * Documentation/dev-tools/kfence.rst.
   5  *
   6  * Copyright (C) 2020, Google LLC.
   7  */
   8
   9 #ifndef MM_KFENCE_KFENCE_H
  10 #define MM_KFENCE_KFENCE_H
  11
  12 #include <linux/mm.h>
  13 #include <linux/slab.h>
  14 #include <linux/spinlock.h>
  15 #include <linux/types.h>
  16
  17 #include "../slab.h" /* for struct kmem_cache */
  18
  19 /*
  20  * Get the canary byte pattern for @addr. Use a pattern that varies based on the
  21  * lower 3 bits of the address, to detect memory corruptions with higher
  22  * probability, where similar constants are used.
  23  */
  24 #define KFENCE_CANARY_PATTERN(addr) ((u8)0xaa ^ (u8)((unsigned long)(addr) & 0x7))
  25
  26 /* Maximum stack depth for reports. */
  27 #define KFENCE_STACK_DEPTH 64
  28
  29 /* KFENCE object states. */
  30 enum kfence_object_state {
  31         KFENCE_OBJECT_UNUSED,           /* Object is unused. */
  32         KFENCE_OBJECT_ALLOCATED,        /* Object is currently allocated. */
  33         KFENCE_OBJECT_FREED,            /* Object was allocated, and then freed. */
  34 };
  35
  36 /* Alloc/free tracking information. */
  37 struct kfence_track {
  38         pid_t pid;
  39         int cpu;
  40         u64 ts_nsec;
  41         int num_stack_entries;
  42         unsigned long stack_entries[KFENCE_STACK_DEPTH];
  43 };
  44
  45 /* KFENCE metadata per guarded allocation. */
  46 struct kfence_metadata {
  47         struct list_head list;          /* Freelist node; access under kfence_freelist_lock. */
  48         struct rcu_head rcu_head;       /* For delayed freeing. */
  49
  50         /*
  51          * Lock protecting below data; to ensure consistency of the below data,
  52          * since the following may execute concurrently: __kfence_alloc(),
  53          * __kfence_free(), kfence_handle_page_fault(). However, note that we
  54          * cannot grab the same metadata off the freelist twice, and multiple
  55          * __kfence_alloc() cannot run concurrently on the same metadata.
  56          */
  57         raw_spinlock_t lock;
  58
  59         /* The current state of the object; see above. */
  60         enum kfence_object_state state;
  61
  62         /*
  63          * Allocated object address; cannot be calculated from size, because of
  64          * alignment requirements.
  65          *
  66          * Invariant: ALIGN_DOWN(addr, PAGE_SIZE) is constant.
  67          */
  68         unsigned long addr;
  69
  70         /*
  71          * The size of the original allocation.
  72          */
  73         size_t size;
  74
  75         /*
  76          * The kmem_cache cache of the last allocation; NULL if never allocated
  77          * or the cache has already been destroyed.
  78          */
  79         struct kmem_cache *cache;
  80
  81         /*
  82          * In case of an invalid access, the page that was unprotected; we
  83          * optimistically only store one address.
  84          */
  85         unsigned long unprotected_page;
  86
  87         /* Allocation and free stack information. */
  88         struct kfence_track alloc_track;
  89         struct kfence_track free_track;
  90 };
  91
  92 extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
  93
  94 /* KFENCE error types for report generation. */
  95 enum kfence_error_type {
  96         KFENCE_ERROR_OOB,               /* Detected a out-of-bounds access. */
  97         KFENCE_ERROR_UAF,               /* Detected a use-after-free access. */
  98         KFENCE_ERROR_CORRUPTION,        /* Detected a memory corruption on free. */
  99         KFENCE_ERROR_INVALID,           /* Invalid access of unknown type. */
 100         KFENCE_ERROR_INVALID_FREE,      /* Invalid free. */
 101 };
 102
 103 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
 104                          const struct kfence_metadata *meta, enum kfence_error_type type);
 105
 106 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);
 107
 108 #endif /* MM_KFENCE_KFENCE_H */